fix(es/codegen): Don't strip necessary escape characters (#7687)

**Related issue:**

 - Closes #7678.

Author: kdy1

crates/swc/tests/fixture/issues-7xxx/7678/input/.swcrc

@@ -0,0 +1,19 @@
+{
+    "jsc": {
+        "parser": {
+            "syntax": "typescript",
+            "tsx": false
+        },
+        "target": "es2015",
+        "loose": false,
+        "minify": {
+            "compress": false,
+            "mangle": false
+        }
+    },
+    "module": {
+        "type": "commonjs"
+    },
+    "minify": true,
+    "isModule": false
+}

crates/swc/tests/fixture/issues-7xxx/7678/input/1.js

@@ -0,0 +1,5 @@
+let str = "\\uD83D\\uDC68\\u200D\\uD83D\\uDE80";
+
+let obj = {
+    "\\uD83D\\uDC68\\u200D\\uD83D\\uDE80": "wrong"
+};

crates/swc/tests/fixture/issues-7xxx/7678/output/1.js

@@ -0,0 +1 @@
+let str="\uD83D\uDC68\\u200D\uD83D\uDE80";let obj={"\uD83D\uDC68\\u200D\uD83D\uDE80":"wrong"};

crates/swc_ecma_codegen/src/lib.rs

@@ -3770,6 +3770,8 @@ fn get_quoted_utf16(v: &str, ascii_only: bool, target: EsVersion) -> String {
 
                             inner_iter.next();
                             next = inner_iter.peek();
+                        } else if next != Some(&'D') && next != Some(&'d') {
+                            buf.push('\\');
                         }
 
                         if let Some(c @ 'D' | c @ 'd') = next {
@@ -3816,8 +3818,10 @@ fn get_quoted_utf16(v: &str, ascii_only: bool, target: EsVersion) -> String {
                                     iter.next();
                                 }
                             }
-                        } else {
+                        } else if is_curly {
                             buf.push_str("\\\\");
+                        } else {
+                            buf.push('\\');
                         }
                     }
                     _ => {

crates/swc_ecma_minifier/tests/fixture/issues/7678/input.js

@@ -0,0 +1,5 @@
+export let str = "\\uD83D\\uDC68\\u200D\\uD83D\\uDE80";
+
+export let obj = {
+    "\\uD83D\\uDC68\\u200D\\uD83D\\uDE80": "wrong"
+};

crates/swc_ecma_minifier/tests/fixture/issues/7678/output.js

@@ -0,0 +1,4 @@
+export let str = "\\uD83D\\uDC68\\u200D\\uD83D\\uDE80";
+export let obj = {
+    "\\uD83D\\uDC68\\u200D\\uD83D\\uDE80": "wrong"
+};